This invention relates generally to touch sensitive systems, and more particularly to identifying locations of two or more simultaneous touches on a touch sensitive system that uses bending-wave touch sensors.
Touch panels are used to provide two-dimensional coordinate information. One example may be an opaque track pad while another example may be a transparent touchscreen placed in front of a display such as a liquid crystal display. Touch panels may be based on a variety of touch technologies including four-wire and five-wire resistive, capacitive, infrared and surface acoustic wave types, as well as bending-wave touch technologies. One example of bending-wave touch technology are the products offered for sale by Elo TouchSystems, a business unit of Tyco Electronics, under the brand name “Acoustic Pulse Recognition” or more briefly “APR”.
In one approach, bending-wave touch systems may detect a single touch based on a tap of an object, such as a key or finger, used to excite bending waves in a substrate. These bending waves induce electrical signals in piezoelectric elements or sensors (piezos) bonded to the substrate. These signals are captured by electronics and processed to determine a set of (X,Y) coordinates of the touch position, such as by using acoustic fingerprint methods to extract touch coordinate information from piezo signals.
Current applications using two-finger gestures such as zoom and rotate require multiple touches to be detected at the same time. Therefore, there remains a need for the detection of at least two simultaneous touches in bending-wave touch systems so that a user may interact with data being displayed, such as graphics and photos, or with programs such as when playing music. The ability to use two or more simultaneous touches would increase the interactive capability of the system. Bending-wave touch panels may be used in, but are not limited to, hand-held devices, desk top and portable computers, geographically fixed applications such as kiosks, large window applications, and the like.